1. Field of the Invention
The present invention relates to a fixing apparatus designed for use in an image forming apparatuses such as copiers or printers and configured to fix developer images on paper sheets.
2. Description of the Related Art
Any image forming apparatus utilizing digital technology, such as an electronic copier, comprises a fixing apparatus. The fixing apparatus has a heating roller and a pressing roller. The pressing roller contacts the heating roller. A paper sheet with a toner image on it can be fed forward through the nip between the heating roller and the pressing roller. As the sheet is so fed, the toner image is fixed on the paper sheet by virtue of the heat generated by the heating roller.
The heating roller generates heat by means of induction heating achieved by a high-frequency magnetic field. The heating roller incorporates a coil and a capacitor connected to the coil. The coil and capacitor constitute a resonance circuit. When the resonance circuit is excited, a high-frequency current flows in the coil. As the current flows in the coil, the coil generates a high-frequency magnetic field. The magnetic field induces an eddy current in the heating roller. The heating roller generates Joule heat from the eddy current.
In any fixing apparatus that performs induction heating is performed, a thermostat is attached to the heating roller and is provided on the power-supply line that connects the fixing apparatus to the commercially available power supply. When the thermostat operates, the power-supply line is electrically cut and the induction heating stops. This prevents the heating roller from being heated to an excessive temperature.
The thermostat cannot operate the moment an excessive heating of the heating roller is detected. Rather, it starts with some time delay. Consequently, the heating roller and its neighboring components may be thermally influenced.
A part of the power line goes around the thermostat provided on the heating roller. This arrangement of the power line is undesirable in view of noise reduction and operation safety.